Crucible for heat treatment of conductive materials



July 21, 1970 H. F. STERLING ETAL 3,520,930

CRUCIBLE FOR HEAT TREATMENT OF CONDUCTIVE MATERIALS Filed Aug. 27. 1968 5 Sheets-Sheet 1 lnvenlors HiNLEY E STERLING wuaeer R. cganq: yDfN/S IM- J. HAZEZM A Home July 21, 1970 H. F. STERLING ETA!- 3,520,930

CRUCIBLE FOR HEAT TREATMENT OF CONDUCTIVE MATERIALS Filed Aug. 27. 1968 5 Sheets-Sheet 2 lnvenlors HENLEY E STERLING W/[BERT R. GEORGE yDEN/J' N, JJIAZELOEN July 21., 1970 H. F. STERLING T L 3,520,930

CRUCIBLE FOR HEAT TREATMENT OF CONDUCTIVE MATERIALS Filed Aug. 27, 1968 5 sheet s -sheet 5 ill! 1P5,

A AL.

Inventors HENLEY F. STERl/UG W/LQERT R. GEORGE yDEN/S W J. HAZEIM A Home July 21, 1970 H. F. STERLING ET'AL Filed Aug. 27. 1968 5 Sheets- Sheet 4 mm H IHITZ HUB .4 Home July 21, 1970 H. F. STERLING ETAL 3,520,980

CRUCI BLE FOR HEAT TREATMENT OF CONDUCTIVE MATERIALS Filed Aug. 27, 1968 5 sheets sheet 5 I 0 HIGH FREQUEN'Q ScuRcF.

63 4 r A-( '45 T Inventors M 3 I Altorne United States Patent US. Cl. 13-27 6 Claims ABSTRACT OF THE DISCLOSURE A crucible for heat treatment of conductive materials is provided by a plurality of vertical tubes spaced closely together to form a wall and having inwardly extending portions to form a bottom. The tubes also provide a passage for cooling fluid therethrough.

This invention relates to apparatus for the heat treatment of electrically conductive materials, having particular application to the melting or other heat treatment of materials which are highly reactive when hot and hence are particularly liable to contamination during treatment by the material of which a containing crucible is made.

According to the invention there is provided a crucible having a wall formed by parallel lengths of tubes of metal of high electrical and thermal conductivity and a floor formed by inwardly extending further lengths of at least some of said tubes, the wall-forming tube lengths and the floor-forming further tube lengths being spaced sufiiciently closely side by side to prevent molten crucible-charge material escaping therefrom, and means for passing cooling fluid through the tubes.

For the purposes of this specification a metal of high electrical and thermal conductivity is defined as a metal having a thermal conductivity of not less than 0.49 gram calories per sec. per cm. per C. per cm. and a specific electrical resistance of not more than 2.665X ohms per cm. at 0 C. Silver, gold and copper are suitable metals, silver being preferred since it can be highly polished to reduce the loss of heat from the charge by radiation. Alloys of these metals may be employed, or a surface coating of one metal such as silver on a member made of another metal such as copper.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIGS. 1A and 1B are respectively a side elevation and an underneath view of FIG. 1A sectioned along X-X, of a first form of crucible,

FIG. 2 is a side elevation of a second form of crucible,

FIGS. 3A and 3B are respectively a side elevation and an underneath plan view of a third form of crucible,

FIGS. 4A and 4B are respectively a partly sectioned side elevation and an underneath plan view of a fourth form of crucible.

FIG. 5 is a side elevation of heat treatment apparatus incorporating any of the four forms of crucible.

Each form of crucible to be described is constructed from silver plated copper tube of A inch outside diameter and gauge wall thickness. Each form of crucible consists of a circular cluster of such tubes spaced sufiiciently closely side by side, e.g., ,6 inch apart, to prevent molten charge material escaping with their axes vertical around the circumference of the crucible. Each 'ice form of crucible has an internal diameter and length such as to contain a charge of about 1 kilogram.

Referring now to FIGS. 1A and 1B, the first form of crucible comprises an annular cooling fluid manifold 1 with an inlet 2 and an outlet 3. Diametrically opposed plates 4 in the manifold separate the inlet chamber 5 from the outlet chamber 6.

Extending from the upper surface of the manifold 1 are twelve tube lengths 7, with one half of the tube lengths communicating with the inlet chamber 5 and the other half of the tube lengths communicating with the outlet chamber 6.

Pairs of tube lengths 7, with one tube length of each pair extending from the inlet chamber 5 and the other tube length of each pair extending from the outlet chamber 6, are formed by separate tubes bent into inverted U-shapes so that cooling fluid may be passed through the tubes. The U-bends are above the charge containing length of the crucible and so arranged that the crucible has a top opening for the charge material.

The floor of the crucible is formed by alternate diametrically opposed lower re-entrant portions 8 of the tube lengths extending inwardly towards each other with the apexes 9 of the reentrant portions defining in combination an unobstructed aperture 10 sufficiently small to prevent solid crucible-charge material passing therethrough.

The required size of the aperture 10 is determined by the solid particle size of the charge material, and is a function of the diameter and number of tube lengths forming the crucible. Provision of the aperture is only necessary when it is required to remove the charge material from the crucible by bottom pouring of the molten charge into a suitable lower container. When there is no such requirement, the apexes of the re-entrant portions may be extended sufiiciently close together by tapering the tubes at this point to prevent any molten material passing therethrough.

The second form of crucible shown in FIG. 2 is constructed very similarly to the first form, except that the wall forming tube lengths 20 are each formed by separate tubes extending between an annular lower manifold 21 and an annular upper manifold 22 for the passage of cooling fluid through the tubes. The inside diameter of the upper manifold 22 is greater than the internal diameter of the hcarge containing volume of the crucible to permit top loading of the crucible. The floor of the crucible is formed by reentrant portions 23 of the tube lengths as in the first form, which may or may not define a bottom pouring aperture between their apexes.

The third form of crucible shown in FIGS. 3A and 3B has both annular manifolds 30 and 31 above the charge containing volume, each manifold having an internal diameter greater than the internal diameter of the charge containing volume to permit top loading of the crucible.

The wall of the crucible comprises twelve parallel tube lengths 32 formed by six separate tubes each connected between the two manifolds so that cooling fluid may be passed through the tubes. Each of the separate tubes extends downwardly from one of the manifolds to form part of the crucible wall, then has a reentrant portion with the inwardly extending part 33 forming part of the crucible floor. The outwardly extending part 34 of the reentrant portion is additionally bent so that the remainder of the tube forms an adjacent wall length, the end of this adjacent Wall length being terminated in the other manifold. As in the first and second forms of crucible, the apexes 35 of the reentrant portions define in combination an unobstructed aperture 36 for bottom pouring of molten crucible charge material, with retention of solid charge material.

In the fourth form of crucible shown in FIGS. 4A and 4B, there are two annular manifolds 40- and 41 above the charge containing volume of the crucible, each manifold having an internal diameter greater than the internal diameter of the charge containing volume to permit top loading of the crucible.

The wall of the crucible comprises twelve parallel tube lengths 42 each formed by a separate tube extending downwardly from the lower manifold 41. Each tube length terminates at the bottom of the crucible in a closed end, with the closed ends 43 of alternate tubes extending towards each other in opposed pairs to define in combination an unobstructed aperture 44 for bottom pouring of molten charge material with retention of solid charge material.

Inside each tube length 42 is a narrower tube 45 terminating a short distance from the closed end of the tube, and passing upwardly through the lower manifold 41 and sealed therefrom to communicate with the upper manifold 40, so that cooling fluid can be passed through the tubes.

In all the above described forms of crucible, the wall forming tube lengths may be flattened on the inside and the outside from a circular section to provide, for a given tube starting diameter, a larger charge containing volume diameter.

When a crucible of one of the forms described above is incorporated in apparatus for the heat treatment of electrically conductive materials, a primary induction coil, appreciably narrower than the length of the charge containing volume of the crucible, encircles the crucible to serve as a source of high frequency current when connected to a suitable power supply to establish circumferential circulating currents in each of the tubes forming the crucible wall, through which cooling fluid, e.g., water, is circulated, and in a charge of conductive material in the crucible, so that the charge is heated over a narrow horizontal zone, if necessary above the charge melting point.

The magnetic fields due to the circulating currents induced in the wall of the crucible and hence in the charge result in mutual repulsion between the molten charge zone and the adjacent surfaces of the crucible. If the current density is sufficiently high the charge is forced away from the adjacent crucible surfaces, and this absence of contact between molten charge and crucible greatly reduces the heat loss from the charge and also virtually eliminates the possibility of charge contamination by the crucible material.

One form of such apparatus may be used for crystal pulling by maintaining the crucible charge material, e.g., silicon, molten at the top of the charge, and withdrawing a seed crystal from the melt.

Another form of apparatus is shown in FIG. for the solid purification of chromium followed if desired by bottom pouring of the purified charge. In FIG. 5, the crucible 50 has been shown only schematically since any of the previously described forms may be used.

The crucible 50 is supported at its upper end in an apertured platform 51 from which extends a chamber 52 having a cover plate 53 which is removable for loading the crucible. There are suitable gas seals 54 and 55 between the chamber 52 and the platform 51 and between the chamber 52 and the cover plate 53 respectively.

Extending from the chamber 52 are a gas inlet (or outlet) pipe 56, and water pipes 57 and 58 connected to the two crucible manifolds 59 and 60 so that water can be circulated through the wall forming tubes of the crucible.

A quartz tube 61 encircles the crucible and extends between a gas seal 62 at the platform 51 and a gas seal 63 at a base plate or table 64. There is a gas outlet (or inlet) pipe 65 extending into the quartz tube, and a container 66 of a suitable material for the reception of the molten charge material from the crucible 50. This container could be a mould for direct pouring,

Encircling the quartz tube is a primary induction coil 67 connected to a high frequency alternating current source 68. Means (not shown) are provided for causing relative axial movement between the crucible and the induction coil 67, either by movement of the coil 67 with respect to the crucible, or by movement of the crucible with respect to the coil 67.

In this particular example, the crucible is loaded with a charge of partly purified chromium in the form of a consolidated mass of irregularly shaped pieces. With the apparatus assembled and sealed as shown in FIG. 5, hydrogen or other gas at a suitable pressure is passed through the pipes 56 and 65 to provide a reducing atmosphere, the primary coil 67 is energized such as to raise the temperature of the chromium in a zone adjacent to the coil to a temperature of about 1400 C., i.e., below the melting point of chromium.

By relative movement of the coil with respect to the crucible, this high temperature zone is traversed along the whole length of the chromium charge, from the botton to the top of the charge, resulting in removal of any trace of oxygen in the chromium in the reducing atmosphere.

After this treatment, the solid charge may be bodily removed from the crucible, or may be poured into the container 66 by locating the coil 67 in line with the bottom pouring aperture in the crucible and raising the temperature of the charge in this bottom region to above its melting point. i

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.

We claim:

1. A crucible having a wall formed by parallel lengths of tubes of metal of high electrical and thermal conductivity and a bot-tom formed by inwardly extending further lengths of at least some of said tubes, the wall-forming tube lengths being spaced sufliciently close side by side to prevent molten crucible-charge material escaping therefrom, the bottom forming further tube lengths being spaced sufiiciently close side by side to prevent solid crucible-charge material from passing therethrough, and

. means for passing cooling fluid through the tubes.

2. A crucible as set forth in claim 1 in which said bottom-forming further lengths are so arranged as to define in combination an unobstructed aperture in the bottom sufiiciently small to prevent solid crucible-charge material passing therethrough.

3. Apparatus for the heat treatment of electrically conductive material including a crucible as set' forth in claim 1, and means for connection to a source of high frequency current to establish circumferential circulating currents in a narrow zone in each of the tubes forming the crucible wall and in a charge of conductive material if present within the crucible.

4. Apparatus as set forth in claim 3 in which the means for connection to a source of high frequency current comprises a primary induction coil surrounding the crucible.

5. Apparatus as set forth in claim 3 comprising means for surrounding the crucible with a desired atmosphere.

6. Apparatus as set forth in claim 3 comprising means for causing the said narrow zone to be traversed axially along the crucible and along a charge of conductive material if present within the crucible.

References Cited UNITED STATES PATENTS Reboux 219-l0.49 X

JOSEPH 'V. TRUHE, Primary Examiner L. H. B'ENDER, Assistant Examiner U.S. Cl. X.R. 2l9-l0.49; 266-39 

